1. Field of the Invention
The present invention generally relates to a compact-size antenna and a personal computer using the same, and more particularly, to a compact-size planar antenna for a wireless communication device which provides high quality and performance by improving signal radiation and receptivity.
2. Description of the Related Art
Development of portable mobile communication terminals for a wireless communication service has been aimed for a wireless terminal (hereinafter a terminal) with more compactness and diversity, and lower power-consumption, and an antenna in such a terminal plays an important role that determines the quality of signal transmission and reception between the terminal and a base wireless station.
In the wireless communication terminal, which has to be compact-sized and at the same time guarantee smooth two-way communication, a non-directional and easy to keep antenna is demanded. Usually, such antennas include helical antennas, monopole antennas or a combined antenna having both the helical and monopole antennas. While the terminals with these antennas almost always have smooth communication without being constrained by the direction where the terminals are placed, the terminals also have the shortcoming of having an upper portion which is jutted out.
In order to solve the antenna jutting out shortcoming, for example a surface-mounted device (SMD) type antenna and a planar antenna have been proposed. These antennas have radiation patterns varying in accordance with design, and provide high portability as they are attachable inside the terminals.
The SMD type antenna is formed in a relatively small volume of space (i.e., micro-sized) by using a general multi-layer substrate and a dielectric fabrication method. In the initial development stage, the SMD type antennas were made in a manner that monopoles and small-size helical antennas are formed by using a high dielectric constant. Currently, however, various SMD type antennas are manufactured based on various pattern technologies. Currently available SMD type antennas mainly include, for example, chip antennas, stacked antennas, and pattern antennas. Being micro-sized, these SMD type antennas are mountable almost anywhere in the wireless communication device. In addition to high productivity, these SMD type antennas are quite advantageous, because they can be directly mounted on a circuit board instead of being built in the wireless communication device. However, these SMD type antennas are constrained by direction when mounted in the terminal body, thus they have bad signal receptivity and a poor radiation pattern.
Regarding a planar type antenna, a planar inverted F antenna (PIFA) is a representative example. The PIFA has a radiation pattern varying in accordance with the design, and also provides high portability because it can be attached to the upper or inner side of the wireless communication device. The PIFA antenna consists of a ground plane, a top-plate, and a feeder or a short-circuit plate. The ground plane is formed slightly larger than the top-plate, and is directly attached to a separate circuit board and inserted inside the side of the wireless communication device.
FIG. 1 is a radiation pattern graph of such a conventional PIFA antenna. As shown, the radiation of the antenna deviates from 0 dB. For example, on average, radiation is −8.70 dB in 2400 MHz, −8.25 dB in 2442 MHz, and −8.45 dB in 2484 MHz, which indicates that radiation pattern is relatively poor.
FIG. 2 is a graph of a voltage standing wave ratio (VSWR) of the conventional PIFA antenna. As shown, the VSWR is 2.5062 in 2.4 GHz, and 2.1995 in 2.442 GHz, which is above level 2 as shown in the graph and indicates not a good condition. The bottom of FIG. 2 indicates impedance of RF property, which is about 63Ω. As shown in FIGS. 1 and 2, the conventional compact-size planar antennas, including the PIFA antenna, have a shortcoming of a bad radiation pattern and a bad VSWR.